I have actually got a bit fed up with the Ultra.
First the USB input rescan didn’t work with additions and deletions.
Then Wiim fixed it, albeit it being awfully slow.
Now after the Ultra update it doesn’t appear to rescan anymore.
I may just return it as it’s somewhat annoying now.
Maybe better just use offboard server. NAS/Pi/PC etc
A full rescan of my 300,000 tracks takes about 8-10 hours, but most of that is the album art downloader/resizer build into LMS. If I disable that it would probably be around 2 hours.
My Kodi box full rescan is slow as well probably a day, not sure I just left the Kodi box running , much much slower than LMS.
Wiim have quad core, so probably fast enough, but the low amount of RAM could be a issue.
Also I have a audio streamer that is much much older than yours, it's basically a box, 99% of the things is UI and server. I could have a Hifi Rose, but if the UI/server is slow/buggy/useless it doesn't matter how great the Rose is.
I'd be happy with a Squeezebox Duet/Wiim pro, those are basically a black box that you don't physically touch. Look at what the Sonos, their latest software has broken it.
A media player scanner is just an additional bonus feature. if it was sold as a music server outright yeah sure, but it's not.
I don't have a Wiim myself.
Oh my SB Touch also has a music scanner/folder scan option with direct USB HDD to the rear, but that is painfully slow also. I tried it to test and determined it's a useless feature due to CPU power on the SB.